This invention concerns a roller for conveying articles in contact therewith.
Heretofor, rubber rollers have generally been used for the conveyor rollers of this type.
Since the conventional conveyor rollers or the like are in direct contact with articles to be conveyed, they have been manufactured mainly with an aim of increasing the mechanical strength and the friction coefficient.
However, these conventional rollers have a drawback that they are damaged in a relatively short period of time during use and become incapable of obtaining smooth and stable conveyance.
For instance, if they are used for conveying plate-like articles such as extended copper coils, a pair of upper and lower rollers are deformed due to the damages caused by lateral edges of plates such that the respective rollers are convexed from the sides toward the lateral center. As a result, the articles to be conveyed run in a zig-zag manner, which further increases the extent of damages at the surface and prevents the rollers from the rotation in a short time.
Further, since the conventional conveyor rollers are sensitive to contaminations, it is difficult to maintain the physical properties of the surface of the rollers at the initial state for a long period of time and, in addition, the friction coefficient of the surface of the roller greatly varies depending on the dry or wet state or deposition of oil droplets.
Accordingly, the friction coefficient fluctuates greatly even in an identical roll depending on the stance of use, whereby such a fluctuation changes the transmission force for driving roller and also the circumferential or rotational speed of a driven roller to inevitably cause variations in the feeding speed and running in a zig-zag way.
The foregoing situations causes a fetal defect of a lengthy roller conveyor or the like.
By the way, it has been known that a composite material prepared by pressure-molding basic rubber material containing fine collagen fibers exhibits a great dynamic friction coefficient in a dry state (refer to Japanese Patent Laid-Open No. 144041/1980). However, such a composite material is intended to increase the dynamic frictional force in an identical state and a relatively great amount of various additives (reinforcing agent and processing aid) are blended for improving the dispersionability and the moldability of the rollagen fibers and for compensating the reduction in the mechanical strength of the molded material caused by the blending of the fibers.
Although the conveyor roller molded from the abovementioned composite material exhibits a predetermined performance under the circumstance of dry condition, the frictional coefficient of the surface is remarkably decreased to spoil the function as the conveyor roller in such a circumstance as oil droplets exist on the surface of the roller.
The present inventors have studied the reason for the foregoing undesired phenomenons and found that process oils used for improving the dispersionability of the fibers cause the elimination of cell structures of the blended fibers. Further, it has been also found that the fluctuation in the frictional coefficient of the surface becomes smaller as the amount of the reinforcing agent such as carbon black and hydrous or anhydrous silicic acid (white carbon), etc. for improving the general physical properties of the rollers is reduced.